1. Field of the Invention
This invention relates to the production of a concentrated tea extract which will remain non-cloudy during prolonged storage at ambient temperatures.
2. Description of the Prior Art
It is well-known in the tea art that aqueous tea extracts contain materials, generally thought to be complexes of tea tannins and caffeine, which either are or become insoluble at temperatures of below about 120.degree. F. (49.degree. C.). Thus, on standing, a conventionally prepared tea extract will become cloudy as the temperature of the extract decreases towards ambient temperatures or below. This clouding problem is more acute as the concentration of tea solids in the extract is increased. Single-strength or ready-to-drink tea beverages will typically contain a concentration of soluble tea solids of about 0.3% by weight. Aqueous tea concentrates which are designed to be diluted with water prior to consumption may have solid concentrations of up to 25% by weight or more. Clouding can also be a problem in aqueous tea extracts which are prepared by reconstituting powdered tea extracts, such as spray-dried tea.
The prior art is aware of precipitation techniques which overcome the clouding problem. U.S. Pat. No. 2,963,368 describes a process wherein a concentrated tea extract is cooled, thereby precipitating an insoluble tannin-caffeine complex and thereafter removing this precipitate from the extract by mechanical means such as centrifugation. A soluble and/or suspending agent (e.g. glycerol and/or gum) is then added to the clarified extract in order to maintain any remaining tannincaffeine complex in solution or suspension.
U.S. Pat. No. 4,315,036 discloses a tea decaffeination process wherein tea extract is cooled to produce an insoluble caffeine-tannin precipitate which is then separated from the extract, decaffeinated and added-back to the extract. The resulting extract would then be further decaffeinated by repeating the cycle in order to obtain a commercially-meaningful degree of decaffeination. This patent also states that tannins which are not derived from tea, such as tannic acid may be used in the process.
U.S. Pat. No. 2,978,328 discloses a process of a frozen tea concentrate which will maintain clarity following reconstitution in water. According to the process a freshly-prepared tea concentrate is combined with a calcium sequestering agent, such as a polyphosphate salt, before the concentrate is cooled and frozen.
U.S. Pat. No. 2,891,866 discloses a process for producing an improved tea product, such as a liquid tea concentrate or dried tea powder, which will not cloud when reconstituted in warm or hot water. The disclosed process adds a calcium salt to a tea extract or derivative thereof in an amount which is effective to produce a precipitate. The precipitate is then removed from the extract and the extract is thereafter concentrated or dried.
U.S. Pat. No. 3,163,539 to Bach discloses a process for an improved tea concentrate or tea powder which is soluble in cold water by subjecting cold-water, insoluble tea substances to treatment in an aqueous solution or slurry of sodium hydroxide. According to this process the pH of the solution or slurry is raised to at least 8.5, preferably at an elevated temperature, until the desired quantity of insoluble substances are solubilized. The resulting solution is then neutralized to a pH of 4.7 to 5.5, cooled and then clarified.